In general, inkjet printers include at least one printhead that ejects drops of liquid ink onto an image receiving surface. The liquid ink can then be ejected directly onto a media surface, or the ink can be ejected onto a surface of an intermediate imaging member and then transferred to media. Some inkjet printers use phase change inks that are in a solid phase at ambient temperature, but transition to a liquid phase at an elevated temperature. The ink droplets solidify to form an image once the ejected ink is on an image receiving surface.
The media in both direct and offset printing architectures can be a continuous media web. In a web printer, a continuous supply of media, typically provided in a media roll, is conveyed by a plurality of rollers that are arranged to guide the media web through a print zone, where a plurality of printheads are positioned to deposit ink onto the web to form images. Beyond the print zone, the media web is gripped and pulled by mechanical structures to enable a portion of the media web to continuously move through the print zone. Tension bars or rollers may be placed in the feed path of the moving web to remove slack from the web to ensure that the web remains taut without breaking.
In continuous-web, direct-to-media printing, a fixing assembly is used after the ink is ejected onto the web to fix the ink to the web. The fixing assembly used depends on the type of ink. For example, when using melted phase change ink to form images, the fixing assembly may include a pair of rollers that defines a nip for applying pressure to the ink and web to spread the ink on the web as the web passes through the nip. The function of the pair of rollers, also referred to herein as a spreader, is to transform a pattern of ink drops deposited onto a web by flattening and spreading the ink drops to make a more uniform and continuous layer. The spreader uses pressure and heat to reduce the height of the ink droplets and fill the spaces between adjacent drops.
One difficulty faced in the operation of the spreader is providing the web and the ink deposited on the web to the spreader at a temperature that enables the ink deposited on the web to be spread uniformly for high image quality. Due to very fast processing speeds at which some continuous feed imaging devices operate, the ink deposited on the web at the print station may be above a suitable temperature range as the image passes through the nip. This high ink temperature results in the ink bleeding into the web and possibly showing through to the opposite side of the media web. Conversely, if the ink cools below the suitable temperature range prior to reaching the spreader, the ink may not be malleable enough to allow for sufficient line spread or adherence to the web. In addition, the ink ejected by the printheads is generally much hotter than the print medium, and, consequently, areas imaged with high ink coverage may exit from the print zone at higher temperatures than the areas of the media web where little or no ink was ejected. Ink that enters the spreader at varying temperatures can cause inconsistent and non-uniform line spread on the web, reducing image quality. Thus, improved media and ink temperature equalization is desirable.